Heretofore many vibratory methods have been devised to measure the weight and/or mass of an object. Many of the prior vibratory schemes rely upon the object to cause a change in frequency of an introduced signal, or upon measuring a change in the natural frequency of the system when the object is added into it. Some of these prior systems can be seen with reference to the following U.S. Pat. Nos.: G. BRADFIELD Pat. No. 3,332,506 Issued: July 25, 1967; H. PATASHNICK Pat. No. 3,926,271 Issued: Dec. 16, 1975; J. L. CHRISTMANN Pat. No. 3,566,678 Issued: Mar. 2, 1971; J. W. FOGWELL Pat. No. 3,572,098 Issued: Mar. 23, 1971; A. WIRTH et al Pat. No. 3,621,713 Issued: Nov. 23, 1971; M. GALLO Pat. No. 3,612,198 Issued: Oct. 12, 1971; and J. L. CHRISTMANN Pat. No. 3,608,359 Issued: Sept. 28, 1971 W. E. THORTON Pat. No. 3,555,886 Issued: Jan. 19, 1971.
The present invention does not rely upon a change in frequency of the system to determine the weight of an object. Rather, the invention contemplates obtaining an output signal, whose frequency is essentially the same as the input signal frequency. The invention measures a change in amplitude of the output signal, the amplitude being a function of the mass. The inventive system uses a piezoelectric crystal to excite the mass into vibrating. Another piezoelectric crystal is used as a detector of the force necessary to accelerate and decelerate (vibrate) the mass. The force necessary to vibrate the mass is proportional to the output voltage of the crystal. A mass determination can be made by knowing the average acceleration and the force (F = ma).